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Thrusting in the lower crust: evidence from the Oygarden Islands, Kemp Land, East Antarctica

Published online by Cambridge University Press:  01 May 2000

N. M. KELLY ,
G. L. CLARKE ,
C. J. CARSON  and
R. W. WHITE
N. M. KELLY
Affiliation:
School of Geosciences, F05, University of Sydney, Sydney, NSW 2006, Australia
G. L. CLARKE
Affiliation:
School of Geosciences, F05, University of Sydney, Sydney, NSW 2006, Australia
C. J. CARSON
Affiliation:
School of Geosciences, F05, University of Sydney, Sydney, NSW 2006, Australia Present address: Department of Geology & Geophysics, Yale University, New Haven, CT 06511, USA
R. W. WHITE
Affiliation:
School of Earth Sciences, University of Melbourne, Parkville, VIC 3052, Australia
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Abstract

Layered orthogneisses of the Oygarden Islands preserve evidence for four high-grade deformation events (D1 to D4). Archaean D1 and D2 structures are only patchily preserved due to extensive recrystallization during D3 and D4, which represent effects of the c. 1000 Ma Rayner Structural Episode. Ductile thrusting at middle to lower crustal levels occurred during D3, which is separated into two mutually cross-cutting phases based on structural geometry; the two phases represent changes in finite strain that developed during progressive deformation. East-directed transport during D3a developed subhorizontal thrusts that contain co-axial, east-trending F3a folds and L3a lineations. Buckling as a consequence of constriction in thrust duplexes developed upright F3b folds coaxial to F3a folds, and steeply south-dipping D3b shear zones. Garnet–clinopyroxene- and garnet–orthopyroxene-bearing assemblages in mafic lithologies, and garnet–sillimanite-bearing assemblages in pelitic lithologies reflect D3 conditions of P=9 kbar and T=800–850 °C. The well-exposed D3 duplex structures indicate that shortening of the lower crust may be accommodated by extensive strain partitioning to develop contemporary kilometre-scale thrust stacking and ductile flow.

Type
Research Article
Information
Geological Magazine , Volume 137 , Issue 3 , May 2000 , pp. 219 - 234
Copyright
© 2000 Cambridge University Press

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